Blasts are not uncommon in the eastern Libyan city, but school attacks are rare

Libyan authorities are struggling to impose order in a country awash with weapons

Tripoli, Libya (CNN) -- Six students were wounded when unknown assailants tossed a hand grenade into a school in the eastern Libyan city of Benghazi, hospital staff said Wednesday.

The blast occurred during break time at the Mahd al-Maarefa school. In a statement on its Facebook page, Benghazi's al-Jalaa hospital said it had received the students, some of them between the ages of 13 and 17.

It quoted a student as saying the hand grenade was thrown into the school from outside its walls, injuring students in the legs.

Blasts and assassinations are not uncommon in Benghazi, the cradle of Libya's 2011 uprising and where U.S. Ambassador Christopher Stevens and three other Americans were killed in an attack on the U.S. diplomatic mission in September 2012.

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But they have mainly targeted security officials. Attacks on schools are rare.

Two and a half years after the fall of Moammar Gadhafi, Libya's weak authorities are struggling to impose order and control heavily armed former rebels, militias and militants who fought to oust the dictator.

Militia brigades often take the law into their own hands as they fight turf wars, and they have refused to lay down their weapons.